How to assign indicies of a function imput vector

I'm trying to write a script to model a SIR epidemic. Matlab is giving me an error (not enough input arguments) when trying to define variables (S, I, R,..) as entries in the function input vector N (S=N(1), etc...).

Here's the script:

 function result=SIR_Model( t, N)

%define probabilities
qi=0.005;
lamda=0.1;
gammaS=0.1;
gammaM=0.009;
pl=0.045;
pj=0.005;
qr=qi/lamda;

S=N(1);
I=N(2);
R=N(3);
Sg=N(4);
Ig=N(5);
Rg=N(6);

%Enter equations
dR=qr*I;
dI=qi*Sg*Ig-qr*I;
dS=-qi*Sg*Ig;
dRg=qr*Ig-pl*(Rg+qr*Ig)+pj*((R-Rg)+qr*(I-Ig));
dIg=qi*Sg*Ig-qr*Ig-pl*(Ig+qi*Sg*Ig)+(1-qr)*pj*(I-Ig);
dSg=-qi*Sg*Ig-pl*(Sg-qi*Sg*Ig)+pj*(S-Sg);

result=[dR, dI, dS, dRg, dIg, dSg];

%use odeXXx to solve DiffEQ

ODE45(SIR_Model, [0,2000], [999,1,0,0,0,0])

[Image Analyst]

How did you call SIR_Model? Also, paste all the red error text - we want the exact error, not a paraphrased one. Because what you said was the error doesn't make sense for the line S=N(1) where you define S. It would make more sense at the function line where you actually enter the function, for example if you called SIR_Model but did not pass in N when you called it.

[Sean Wu]

Sorry, was calling it wrong. Here're the errors:

 ode45(@SIR_Model, [0,1000], [999, 1, 0,0,0,0])
  Error using feval
  Undefined function 'SIR_Model' for input arguments of type 'double'.

Error in odearguments (line 88)
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.

Error in ode45 (line 114)
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn,
...

[Sean Wu]

This fixed the errors:

 N=[999,1,0,0,0,0]
  ode45(@SIR_Model, [0 1000],N)

Thanks for your help

Answer 1

[Walter Roberson]

Change

ODE45(SIR_Model, [0,2000], [999,1,0,0,0,0])

to

ode45(@SIR_Model, [0,2000], [999,1,0,0,0,0])